Copper miners grapple with arsenic problem – by Xan Rice (Financial Times – April 30, 2014)

New flow of ‘dirty’ copper pushing up treatment costs

In the world’s driest desert in Chile, arsenic has long been a hazard. Research published this month revealed that a 1,000-1,500-year-old mummy found in the Atacama region, north of the country, died from drinking water laced with the poisonous element. Today, the threat is less to human life than to the profitability of copper miners.

Arsenic is often found alongside the red metal on the west coast of South America, home to the world’s largest copper reserves. Until recently, mining companies there chose not to develop copper deposits containing high amounts of arsenic, in favour of the abundant cleaner operations.

But as the large, old mines have become depleted, some arsenic-rich sites are now being exploited. They include Toromocho in Peru, which is owned by the Chinese state-owned group Chinalco, and Codelco’s Ministro Hales project in northern Chile. Both are important sources of new global greenfield copper supply.

The new flow of “dirty” copper concentrate is a sign of the declining ore grades globally, and presents fresh challenges for the industry since the material cannot be sent directly to smelters. Delays in processing this concentrate has resulted in stocks increasing and a rise in treatment and refining charges.

Arsenic presents health and safety risks for the smelters that refine copper concentrate – the most basic copper product. Most smelters will not process material containing more than 0.5 per cent arsenic.

Indeed, China, the world’s biggest copper consumer, will not allow the import of concentrate with arsenic levels above this threshold.

At Toromocho, efforts to reduce the arsenic content from more than 1 per cent to 0.7 per cent during production has cut the copper grade in its concentrate from an expected 26 per cent to about 22 per cent, according to Macquarie.
And even then, the arsenic content remains too high for import into China.

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